Abstract

The detection of circulating tumor cells (CTCs) in breast cancer is strongly associated with disease relapse. Since it is unclear if all CTCs are capable to generate metastasis, we investigated their apoptotic and proliferative status in 56 CTC-positive (29 early and 27 metastatic) breast cancer (BC) patients. Double staining immunofluorescence (IF) experiments were performed in peripheral blood mononuclear cells (PBMC) cytospins, using the pancytokeratin A45-B/B3 antibody and either M30 (apoptotic marker) or Ki67 (proliferation marker) antibodies. Apoptosis was also evaluated using a polycaspase detection kit. Patients with metastatic disease had significantly lower numbers of apoptotic CTCs compared to early breast cancer patients (polycaspase kit: 8.1% vs 47.4% of the total CTC number; p=0.0001; M30-antibody: 32.1% vs 76.63%; p=0.002). The median percentage of apoptotic CTCs per patient was also lower in patients with advanced compared to those with early disease (polycaspase kit: 0% vs 53.6%; M30-antibody: 15% vs 80%). Ki67 positive CTCs were identified in 51.7% and 44% of patients with early and metastatic disease, respectively. Adjuvant chemotherapy reduced both the number of CTCs/patient and the number of proliferating CTCs (63.9% vs 30%). In conclusion apoptotic CTCs could be detected in patients with BC irrespectively of their clinical status, though the incidence of detection is higher in early compared to metastatic patients. The detection of CTCs which survive despite adjuvant therapy implies that CTC elimination should be attempted using agents targeting their distinctive molecular characteristics.